A fill-up control valve device is known in the art, for example, as disclosed in Japanese Patent Publication No. 2004-257264 (corresponding to U.S. Pat. No. 6,994,103 B2). The fill-up control valve device has a float valve unit which is arranged in a casing attached to a fuel tank, wherein the floating valve unit floats on liquid fuel. When a fuel liquid level in the fuel tank is raised and reaches at a first predetermined level (which corresponds to a fuel filled-up level), the liquid fuel enters the casing through a ventilation hole (a first ventilation hole) formed at a lower end of the casing. Then, the fuel liquid level in the casing is raised up to a second predetermined level, which is higher than the first predetermined level, so that the float valve unit is floated up and seated on a valve seat formed at an upper portion of the casing. As a result, a ventilation passage for communicating an inside of the fuel tank with an outside thereof is closed.
As above, when the liquid fuel is fed into the fuel tank from a fuel feeding port and the fuel liquid level in the fuel tank is raised to the fuel filled-up level, inner pressure of the fuel tank is increased so that a fuel liquid level in a fuel feed pipe is raised up to a portion close to the fuel feeding port. Then, a fuel feeding operation of a fuel feeding gun is automatically stopped by an automatic fuel stop mechanism of the fuel feeding gun. Therefore, additional fuel feed, which would raise the fuel liquid level higher than the fuel filled-up level, is prevented.
In the above filled-up control valve device, another (second) ventilation hole having a small diameter is formed at the casing at such a portion higher than the above second predetermined level, for the purpose of reducing pressure fluctuation in the fuel tank after the liquid fuel is filled up in the fuel tank. According to such a structure, an inside space of the fuel tank and an inside space of the casing is communicated with each other through the second ventilation hole.
According to the above filled-up control valve device, when the fuel liquid level in the fuel tank reaches at a lower end of the casing (that is, almost the fuel filled-up level), the pressure in the inside of the casing becomes relatively lower than the pressure in the inside of the fuel tank, and thereby the fuel liquid level in the casing is raised by the increased pressure in the inside of the fuel tank and the float valve unit finally closes the ventilation passage. However, since the second ventilation hole is formed at the casing at such a position higher than the second predetermined level which is raised in the casing, the pressure in the casing and the pressure in the fuel tank are gradually counterbalanced. Then, the liquid fuel in the casing is discharged through the first ventilation hole formed at the lower end of the casing, so that the ventilation passage is opened by the float valve unit in a relatively short period since it has been closed. As a result, the inner pressure of the fuel tank is decreased. Then, the fuel liquid level in the fuel feed pipe may be lowered from the fuel feeding port. It is, therefore, a problem that additional fuel feed may become possible even in the case that the fuel tank is filled up with the fuel. It is desirable that the time period for keeping the valve closed condition of the float valve unit may be elongated in order to surely prevent the additional fuel feed after the filled-up condition in the fuel tank.